Cements and cement structures are commonplace—both in industrial applications and in everyday life. For example to recover natural resources such as gas, oil, and water residing in subterranean formations or zones a wellbore is drilled down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby pipe strings such as casings and liners may be cemented in well bores. In performing primary cementing, hydraulic cement compositions may be pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore.
A cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Once set, a cement sheath may be subjected to a variety of cyclic, shear, tensile, impact, flexural, and/or compressive stresses that may lead to failure of the cement sheath. Such failure may be the result of fractures, cracks, and/or debonding of the cement sheath from the pipe string and/or the formation. Undesirably, cement-sheath failure may lead to loss of zonal isolation, resulting, for example, in the undesirable migration of fluids between formation zones. This may lead to undesirable consequences such as lost production, costly remedial operations, environmental pollution, hazardous rig operations resulting from unexpected fluid flow from the formation caused by the loss of zonal isolation, and/or hazardous production operations. Furthermore, failure of the cement sheath also may be caused by forces exerted by shifts in subterranean formations surrounding the well bore, cement erosion, and repeated impacts from the drill bit and the drill pipe.
Subsequent secondary cementing operations may also be performed. One example of a secondary cementing operation is squeeze cementing whereby cement slurry is employed to plug and seal off undesirable flow passages in the cement sheath and/or the casing. Cement compositions also may be used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Cement compositions utilized in subterranean operations may be lightweight to prevent excessive hydrostatic pressure from being exerted on subterranean formations penetrated by the well bore, whereby the formations may be unintentionally fractured. In some environments, cementing operations may need lightweight cement slurries having reduced densities (e.g., a low-density slurry). For instance, cementing across highly depleted zones and weaker formations may need lightweight cement for sufficient circulation. If the cement cannot be successfully circulated, the desired level of annular fill may not be achieved, and consequently the desired seal may not be achieved. As a result, a large impact on the drilling cost may be experienced and delays in production delivery may occur due to the remedial work.
Cements are also commonly utilized above ground structures e.g., in construction, transportation and other industries. Examples of common above ground structures and materials made from cement include, but are not limited to, building materials (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster); transportation materials, (roads, pathways, crossings, bridges, sleepers, viaducts, tunnels, stabilization, runways, parking); water conduits (pipes, culverts, curbing, drains, canals, weirs, dams, tanks, pools); support structures (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing); agriculture structures (buildings, processing, housing, feedlots, irrigation); and even art objects (statues, sculptures, and statuaries). Each of these uses can benefit from the use of lightweight cement compositions.
One type of lightweight cement composition is a foamed cement composition, i.e., a cement composition that comprises a gas. The use of foaming agents to provide lightweight cement compositions was first shown in the early 1980's in, for example, U.S. Pat. Nos. 4,300,633 and 4,333,764. Subsequently, foamed cements, the use of foamers, and foam stabilizer based surfactant systems have been the subject of several patents. See, e.g., U.S. Pat. Nos. 5,711,801; 5,803,665; 5,897,699; 5,900,053; 5,966,693; 6,063,738; 6,227,294; 6,244,343; 6,336,505; 6,364,945; 6,367,550; 6,547,871; 6,797,054; 6,619,399; 6,955,294; 6,336,505; 6,953,505; 6,835,243; 7,008,477; 7,013,975; 7,191,834; 7,373,981; and 7,607,484 as well as in US Published Application 2010/0077938 A1. In addition to being lightweight, the gas contained in the foamed cement composition may improve the ability of the composition to maintain pressure. In subterranean applications, such as in wells, this prevents the flow of formation fluids into and through the cement composition during its transition time, i.e., the time during which the cement composition changes from a true fluid to a set mass. Foamed cement compositions may be advantageous because they can have low fluid loss properties and may act to prevent the loss of fluid during circulation. Additionally, foamed cement compositions when set should have a lower modulus of elasticity than non-foamed cements, which is often desirable as it enables the resultant set cement, inter alia, to resist hoop stresses exerted on the set cement in the annulus.
Lightweight and/or foamed cements have been prepared in a variety of ways, for example, by addition of water, microspheres or gas to the cement. See, e.g., the patents and published application cited above. Drawbacks to addition of extra water to the cement include reduced efficiency in solidifying of the cement. For instance, the additional water may dilute the cement and thereby extend the time at which the cement may set. Drawbacks to using microspheres include costs associated in adding a sufficient amount of microspheres to reduce the density of the cement to lower than typical densities. Drawbacks to adding gas include excess permeability at high gas concentrations. Consequently, there is a need in the art for an improved foamed cement composition for use both above ground and in subterranean environments.
When cement is used, a slurry of the cement dry components is prepared then poured into place and cured (hardened). The curing can take time. Additives known as accelerators are often added to accelerate cement's cure (or set) time and improve cure characteristics of the cement. Alkali silicates have been widely used as an accelerator for cements and concrete. They are seen as the most effective alkaline activators for cementing systems in general. Alkali silicates are also used in soil grouting in construction and sweep modification using gas/foam and gel formation in oil field applications. See, e.g., US Published Patent Application 2010/0038085. Silicates are also commonly-used in cementing operations to control cement density and set time. Silicates are used to overcome the negatives associated with water channeling, which are caused by the thinning of the cement slurry when water is added alone. As a water-based extender, the silicate reacts with calcium hydroxide in the cement slurry and produces a viscous gel. The water in the cement then becomes ‘tied up’ in the gel, allowing additional water to be added to the system. The density of cement slurry can also be extended or lowered by adding nitrogen gas or air or additives that forms gas to make extremely lightweight cement systems with preferred mechanical properties. Application rates for silicates in these applications are on the order 3% of the cement weight. Additionally, powdered aluminum or silicon metal have been used in various lightweight cementing applications. Silicates, particularly sodium silicate, are also used in soil cements for grouts. Such uses of silicates are described, for example, in U.S. Pat. Nos. 3,706,581; 4,333,764 and 4,300,633.
Cements, however, are quite complex. Applying these silicates is an art that typically requires many different additives and combinations to yield cement properties for each particular job depending on cost and logistics. Thus, there remains a need for cements and concretes containing silicates which may be easily dispersed in the cement without the requirements for such additives and combinations. This invention answers those needs.